Semiconductors are widely used in integrated circuits for electronic applications, including radios, computers and televisions. Such integrated circuits typically use multiple transistors fabricated in single crystal silicon. A feature of semiconductors that make them so useful for electronic devices is that their conduction properties may be changed by introducing small quantities of dopant atoms.
Ion implantation is a method of introducing dopants into semiconductor surfaces. Ion implantation introduces impurities into a semiconductor wafer by accelerating ions to a high velocity and directing them towards the wafer surface. The dopant atoms enter the crystal lattice of the wafer, collide with surface substrate atoms and gradually lose energy, finally coming to rest at some depth within the lattice. During ion implantation, ions travel in a relatively straight path initially, then travel in a zigzag path during which nuclear collisions absorb energy until they stop moving and settle into the solid at a particular range. Each ion is subject to a slightly different set of conditions and thus has a different range.
When devices such as, for example, transistors, thyristors, diodes, etc., are formed in a semiconductor surface, active areas or mesas are created. These mesas may be doped in a subsequent step by ion implantation.